Spacecraft, such as satellites, typically use attitude and/or momentum control systems, such as control moment gyroscopes (CMG) and reaction wheel assemblies (RWA), for positioning and rotation. CMGs operate by producing a relatively large torque along a first axis when a spinning rotor is rotated with a smaller torque about an axis perpendicular to the rotor spin axis. Accordingly, combinations of CMGs (usually three or more in an array) may be arranged in non-coincidental mounting planes so that the torques may be applied, using various combinations, in any desired direction of rotation. CMGs are most commonly used where large and/or rapid motions, or high inertia equipment, need to be moved with high precision such as in spacecraft slew maneuvers. In contrast, RWAs include a spinning rotor that exerts a relatively small torque along the spin axis as the rotor is caused to spin faster or slower. RWAs may be disposed with several reaction wheels (usually three or more in an array) aligned to cause rotation in any direction. RWAs are usually used where smaller movements are necessary, such as controlling the direction of scan of a sensor, or detector, such as small camera or radar antenna in spacecraft, which operate to view areas or targets on the earth. RWAs are also used to store momentum that is built up by small externally applied torques acting over a long period of time.
Although conventional CMGs and RWAs operate well in many spacecraft, it has been found that both operate less effectively when disposed within a small spacecraft, such as in those spacecraft weighing less than 150 kg. Small spacecraft, increasingly being used to deliver large payloads, may have limited space for containing spacecraft components and thus, the CMGs and RWAs employed therein are smaller. However, smaller-sized CMGs and RWAs may not provide enough torque that may be preferable for moving the payload with the desired agility.
Accordingly, it is desirable to have an attitude and/or momentum control system that is capable of providing an adequate amount of torque to move a large payload. In addition, it is desirable for an attitude and/or momentum control system to be capable of being implemented into a small spacecraft. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.